This invention pertains to improved rheologically-dynamic elastomeric compositions, and more particularly to a composition made using a naphthenic oil carrier and one or more rheology modifiers for improved rheological behavior as a function of temperature.
A rheologically-dynamic fluid applied elastomeric composition having usefulness for waterproofing and other applications was taught in U.S. Pat. No. 5,763,014 of Pickett, which is incorporated herein by reference. The composition of Picket may be characterized as being xe2x80x9crheologically-dynamicxe2x80x9d because the intermixing of two components A and B initiated a number of rheological transformations. Component A comprised an aqueous rubber latex (e.g., styrene butadiene latex, natural rubber, styrene butadiene styrene, butyl rubber, neoprene, nitrite rubber, acrylate, and the like may be used, along with known emulsifying or latex stabilizing agents). Component B, on the other hand, comprised an oil carrier in which were dispersed both a hygroscopic agent and vulcanizing agent. Upon intermixing, component A and B formed a water-in-oil blend wherein the hygroscopic and vulcanizing agents were located in the continuous oil carrier phase, and the rubber was dispersed as droplets in a discontinuous water phase. The respective locations of these components set up a dynamic reaction system: the rubber contained in the aqueous environment of the latex became swelled by the oil carrier, while the hygroscopic agent contained in the oil carrier became chemically bound with the water in the discontinuous aqueous phase. Both factors contributed to the gradual stiffening (e.g., increased viscosity) of the component mixture, and facilitated the initiation of a third process: the vulcanizing agent or agents contained in the continuous oil carrier phase became introduced to the rubber in the discontinuous aqueous phase of the latex, resulting in the hardening of the composition into a solid elastomeric mass. The composition thus provided, at the outset, a flowable or sprayable liquid which could be applied in substantial thicknesses, and which was transformed into a hardened thickness of mass without requiring repeated coatings or applications.
The present inventors sought to improve upon the rheologically-dynamic elastomeric composition taught by the ""014 patent. As a starting point, they focused their attention upon the flowability characteristic of the composition as a function of temperature, and how this relationship might be modified in view of the rheological phenomena and dynamic component inter-relationships discussed above. It was during applications of the composition as a waterproofing coating on outdoor building surfaces that they began to realize that the flowability characteristics of the composition were affected in an unusual way, and this was particularly evident at low temperatures. When data was gathered, and the viscosity of the composition was measured as a function of temperature, it was found that viscosity was not consistent over the temperature range of 40-100xc2x0 F. As shown in FIG. 1, the composition (of the ""014 patent) exhibited a highly desirable viscosity characteristic within the range of about 70-93xc2x0 F. Above and below this temperature range, however, the changes of viscosity over temperature were less predictable. In particular, the composition became increasingly difficult to apply as a coating due to its rapidly accelerating stiffness. Thus, the present inventors realized that an improved elastomeric composition would be desirable because it would allow greater application and usage possibilities over a greater temperature range.
The task of reformulating elastomeric compositions, such as changing rheology modifiers, is hardly a routine matter, particular for dynamic two-phase systems as in the present case. For example, an incorrect substitution of one or more rheology modifiers might cause the rubber particles to remain phase-separated from the oil carrier. This might result, on the one hand, in a two-phase product. Incorrect substitutions might also cause, on the other hand, rubber particles to be transferred too quickly into the oil phase, resulting in an overly-rapid acceleration of viscosity.
As an improvement of two-component, rheologically-dynamic elastomeric formulations of the kind disclosed in U.S. Pat. No. 5,763,014 of Pickett, the present invention achieves a substantially extended linear viscosity behavior as a function of temperature. The new formulations of the present invention not only provide better control over composition viscosity, but also the transfer rate of rubber particles from the aqueous droplets (of the discontinuous latex phase) into the oil carrier (continuous phase). This improved control over rheology dynamics is accomplished by substituting the aromatic/paraffinic oil taught by Pickett ""014 with a naphthenic oil (e.g., containing predominantly naphthene oil in an amount of at least 40 wt. % based on total weight of oil carrier). To enable high levels of naphthene oil to be employed, the present inventors employed an organic rheology modifier in the oil carrier phase (e.g., component B) that provided a thixotropic structure whereby solids could be suspended in the oil phase.
Exemplary organic rheology modifiers suitable for use in the invention include a modified castor oil, a polyamide, a branched or straight chain alkylene group having a molecular weight of 1000-100,000, calcium sulfonate, a modified urea, or a mixture thereof. Modified castor oil is most preferred.
Other exemplary compositions further comprise an inorganic rheology modifier, such as an activated clay. Activated clays may be obtained by treating smectite clay (e.g., bentonite, hectorite, etc.) with a clay-activity modifying agent such as a quaternary amine.
One surprising improvement obtained by the novel combination is that, when viscosity (V) is measured as a function of temperature (T), an extended and substantially linear slope defined by (dV/dT) can be attained. The viscosity behavior of the system demonstrates a linear behavior over a greater temperature range (e.g., dV/dT more consistent over range of 40-100xc2x0 F.) than previously achieved by two-component, dynamically rheological elastomer systems.
An exemplary elastomeric formulation of the invention thus comprises: components A and B which are combinable to form a blend in which a vulcanizing reaction is initiated for solidifying the components into a solid mass; component A thereof comprising an aqueous latex of natural or synthetic rubber; and component B thereof comprising an oil carrier in which is dispersed a vulcanizing agent operative to cure the component A rubber, and component B further comprising a hygroscopic agent operative to chemically bind the water in component A; the component A and B being operative when intermixed to form a water-in-oil blend whereby the oil carrier containing the hygroscopic agent and vulcanizing agent provides a continuous phase wherein an aqueous phase of component A containing the rubber is dispersed therein as a discontinuous phase, the respective locations of the hygroscopic agent, vulcanizing agent, and rubber thereby providing a reaction dynamic wherein the rubber becomes swelled by the oil and the hygroscopic agent chemically binds water in the latex discontinuous aqueous phase, thereby effectuating an increase in viscosity of the intermixed components and enabling the vulcanizing agent and rubber to be introduced to each other such that curing can be achieved at a time later than said viscosity-increasing effectuation; the oil carrier of component B comprising: (a) a napthenic oil in the amount of 40-90% by total weight of the oil carrier; and (b) an organic rheology modifier, preferably a modified castor oil, in the amount of 0.4%-3.5% by total weight of the oil carrier.
In other exemplary formulations of the invention, an inorganic rheology modifier, such as a modified clay, is employed to further improve the rheological behavior of the formulation as a function of temperature.
In addition to the novel formulation compositions described above, the present invention also provides methods for making elastomeric compositions.